1. Field of the Invention
The present invention relates to an image stabilization control apparatus and an imaging apparatus configured to correct or prevent an image shake or image degradation occurring due to vibration such as hand shake.
2. Description of the Related Art
In recent years, all operations of a camera significant to shooting, such as an operation for determining the exposure and a focusing operation, may be automatically performed. Accordingly, even a user who is not accustomed to using a camera may very rarely fail in photographing.
In addition, a recently marketed camera includes an image stabilization control apparatus, which includes a vibration correction unit, a driving unit, and a vibration detection unit and is configured to prevent an image shake occurring due to vibration. By using such a recent camera, a photographer may rarely fail in photographing.
An image stabilization control apparatus configured to prevent an image shake is briefly described below. The hand shake that may occur on a camera during shooting is vibration of, usually, 1 to 10 Hz frequency. To take a photograph without any image shake even when such vibration is applied to a camera when the shutter release button is pressed, it is necessary to detect the vibration applied to the camera and displace a lens for correcting an image shake (hereinafter simply referred to as a “correction lens”) according to the detected value.
Therefore, to shoot an image without any image shake even when camera is vibrated, it is necessary to detect a precise level of the vibration on the camera and to correct the variation in the optical axis occurring due to the vibration. The vibration (on a camera) can be calculated, in principle, by using a vibration detection unit provided on the camera. More specifically, such a vibration detection unit detects the acceleration, the angular acceleration, the angular velocity, and the angular displacement and executes an operation on an output thereof to correct an image shake.
Under a general shooting condition, angular vibration (rotational vibration), which may occur according to the orientation of the camera, is the primary cause of the possible vibration. Therefore, a conventional camera includes an angular velocity meter only to detect vibration. In such a camera, it is intended that an image shake be suppressed by driving a vibration correction unit (i.e., a correction lens), which displaces the optical axis according to a signal from the vibration detection unit, with a driving unit.
Meanwhile, when an image is taken at a close distance (under a shooting condition in which a high imaging magnification is used), a significant image degradation due to parallel vibration, which may otherwise cause little image degradation, may occur in addition to angular vibration, which may occur due to the orientation of the camera. Under a shooting condition in which an object image is taken at such a close object distance as about 20 cm as in the case of macro photography, or if the focal length of an imaging optical system is very large (400 mm, for example) even when a sufficient object distance of 1 meter is secured, it becomes necessary to positively detect the parallel vibration and drive the vibration correction unit.
In this regard, in a method discussed in Japanese Patent Application Laid-Open No. 07-225405, an acceleration meter (acceleration sensor) configured to detect an acceleration is provided to detect parallel vibration and drive a vibration correction unit according to the detected parallel vibration value and an output from an angular velocity meter, which is separately provided.
Furthermore, a method discussed in Japanese Patent Application Laid-Open No. 2002-359769 corrects an image shake while changing the amount of correcting the vibration. In this method, an image sensor of a camera acquires motion information of a taken image while correcting the image shake. This method sets an optimum vibration correction amount by evaluating the accuracy of correcting an image shake according to an output from the image sensor.
In this regard, however, in the method discussed in Japanese Patent Application Laid-Open No. 07-225405, an output signal from the acceleration meter, which is used in detecting parallel vibration, may vary due to disturbance noises or environmental variation such as temperature change. Accordingly, it is difficult to highly accurately correct parallel vibration with this method.
Furthermore, in the method discussed in Japanese Patent Application Laid-Open No. 2002-359769, it takes a long time before setting an optimum vibration characteristic. Accordingly, the user operability of the camera may degrade. In addition, a large size mechanism of the vibration correction unit may become necessary to implement vibration correction using a variable vibration correction amount.